Numerical control of machine tools is a well-developed art, and it developed at a time prior to the development of PC (personal computer) computer systems based on the 8088 microprocessor chip. Numerical control was developed by reference to special computer language or codes especially suitable to machine tool applications. One popular code is called ASCII, and an earlier but still used code is EIA. Both of these codes are based on 8-bit words and are parity controlled. The numerical control languages are not directly compatible to the signal output system characteristic of a PC type computer system. Such a system uses an 8-bit word controlled by a strobe signal.
At the time numerical control for computer systems was developed, the technology most feasible for storing and transmitting the part programs for use in a numerical control system was paper tape, that is, tape formed of relatively strong paper having holes punched in it in a pattern to stand for the numbers involved in the code. The tapes were either read right at the machine tool by a tape reader, or read at some remote location by such a reader, with the signals being transmitted to the numerical control unit of the machine tool by cable. In any event, the paper tapes were fragile and bulky, as well as being slow to read and process.
With the advent of PC types computer systems, based on the 8088 micro-processor chip, it has become desirable to take advantage of the computing power, speed and flexibility of a PC type system in control of machine tools. However, because of the vast number of numerically controlled machine tools in the field, and the huge library of tapes punched according to the popular NC codes, there is a large practical barrier to the usage of PC type computer systems in machine tool applications.
Accordingly, it is an object of the present invention to provide an inexpensive and effective system for making use of a PC type computer to control numerically controlled machine tools, and to make it possible to do away with, or at least retire into back-up libraries, the fragile and troublesome paper tapes hitherto employed for numerical control of machine tools. At the same time, however, it is possible to revert back to paper tape control of a given machine if that is desired in particular instances. Also, in accordance with the invention, it is possible to convert a paper tape library into a library of numerical controlled part instructions on the disk storage media characteristic of a PC type computer system.
An advantage of the invention is that it employs the inexpensive, efficient and effective PC type computer systems which are currently highly popular.
In accordance with the invention, a system for controlling a machine tool by the use of a PC type computer system is provided which includes switching means for selectively inserting an inverter timing board for conditioning signals into circuit position between a PC controlled system and the tape reader, or tape reader interface, of a numerically controlled (NC) or computer numerically controlled (CNC) unit of a machine tool.
Further in accordance with the invention, the inverter timing board is itself a system for controlling the machine tool which is adapted to be responsible to numerical control tape code signals from a computer of the PC type, which is adapted to store process and send signals in computer code.
The inverter timing board includes means for receiving parallel output bit signals from the parallel port of the computer system.
It further includes means for receiving a strobe signal from the parallel port of the same computer.
The inverter timing board includes time delay means actuatable by the strobe signal from the computer for conditioning the steady but strobable high and/or low bit signals from the parallel port of the computer into square wave signals having wave forms of selected time length conforming to the standards of the numerical control tape code being used, such as ASCII or EIA.
The inverter timing board also includes means for transmitting the conditioned square wave signals so produced to the machine tool, and in particular to the tape reader or tape reader interface of the NC control system of that machine tool.
Further in accordance with the invention, the transmitting means mentioned above preferably comprises an "and" gate for each bit signal, which gate generates an output signal upon input of a bit signal and also a signal from the time delay means.
Also in accordance with the invention, it is preferred that the transmitting means include inverter means for each conditioned square wave bit signal.
Further in accordance with the invention, the inverter means are preferably exclusive "or" gates having an input from the before-mentioned time delay means.
There is also provided, in accordance with the invention, an overall system for controlling a machine tool adapted to be responsive to numerical control tape code signals which includes a computer adapted to store, process and send signals in strobable computer code together with means for receiving parallel output bit signals from the parallel port of a computer and means for receiving a strobe signal from the parallel port of said computer. There are also time delay means actuatable by said strobe signal for conditioning the steady but strobable high and/or low bit signals from the parallel port of said computer into square wave signals having wave forms of selected time length conforming to said numerical control tape code and means for transmitting said conditioned square wave signals. Further, the system includes numerical control equipment for receiving, processing and applying said conditioned square wave signals to thereby direct movements of said machine tool.
This system preferably also includes means for transmitting signals derived directly from a paper tape to said numerical control equipment and means for selectively connecting one or the other of said conditioned wave transmitting means and said paper tape signal transmitting means to said numerical control equipment.